Light-impulse system



LIGHT IMPULSE SYSTEM Filed Deo. 22,

Patented ct. 1946 LIGHTfllVIPULSE SYSTEM Victor H. Fraenckel and Siegfried Hansen, Sehenectady, N. Y., vassignors to General Electric Com-pany, a corporation of New York Application December 22, 1941, Serial No.423,984

'10 lClaims.

1 The present invention relates primarily to iinprovements in apparatus Afor locating objects and measuring distances by the transmission and reflection of light-impulses, that is to say, by im pulses of electromagnetic waves within the visible or near-visible range.

It is a primary object of the invention to provide in such apparatus an improved light-impulse generator which is capable of meeting the requirement that the duration of the generated impulses shall be a small fraction of the time required for the reflection of the impulses from an object positioned at any material distance from the impulse source.

It is a further object to provide a generator adapted to produce light-impulses of extremely high instantaneous intensity.

In the attainment of the foregoing objects an important feature of the invention consists in the use of electrodes adapted to sustain an intense spark-discharge in combination with a charge-storing agency which is of such character and which is so connected to the electrodes that the resultant circuit represents a discharge system oi extremely small inductance. By alternately charging an appropriately constructed eiiective duration of less than one-tenth microsecond but which are nevertheless of suiiicient intensity to be reflected in Ydetectable amounts from objects at a distance of many miles. Because of the extreme brevity of the impulses involved, the location of such objects can, with the assistance of a detecting system responsive to such impulses, be determined with'an error of only a few feet, and even higher accuracies are possible under favorable conditions.

The features of the invention which we desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with its further objects and radvantages, thereof may best be understood byreference to the following description Ytaken in connection with the drawing in which Fig. 1 represents schematically a distance-measuringsystem suitably embodying the invention; Figf2 is a sectional view oi a light-impulse generator of Ythe type which characterizes the invention; Fig. 3 is a sectional view taken on line 3 3 of Fig. 2; and Fig. l is a cross-section of one ofthe condenser units of Fig. 2.

Referring to Fig. l there is shown a distancemeasuring system which includes as its maior elements alight-impulse projecting device, a de' vice for receiving Vand detecting the projected light-impulses as Ythey are reflected from a distant object, and means for visibly indicating the time required for the reflection of the light-impulses so as to proyide Aa measure of the distance to the reflecting object.

The light-projecting device comprises in its general aspects a, light-impulse generator i0 and a reflector H for focusing ,in a narrow beam the light radiations developed by the gener-ator. The light-receiving means consists of a focusing mirror I3; preferably of parabolic form, and a lightsensitive agency I4, typically a photocell, arranged at `the focal point of the mirror. The transmitting vand Vreceiving means are preferably oriented 'm `the same direction and are arranged to have their orientation varied simultaneously both in elevation and yin azimuth in order that the surrounding space may be scanned for re.- ecting objects such, for example, as distant aircraft.

`The distance-indicating means comprises a cathode .-ray tube I8, `of which only the screen portion is illustrated in Fig. 1. This tube is of conventional `character and includes means'for generating an electron Abeam and .additional means for Ade iiecting the beam in mutually perpendicular directions to `cause Aa 4confipiexftrace to be developed on the screen of the tube. {Ihe operation of the tube is controlled by Vmea-ns responsive both to the transmission and reception of light-impulses developed-by the generator l0, the nature of the means used in this connection being explained lmore 'fully hereinafter. y

In the use of the apparatus as s o far described the generator lo is actuated in such fashion as to cause it to produce a series of regularly spaced light-,impulses of short duration. AS each impulse is generated it is caused-through the agency of a photosensitive element 2,53 .(e.V g. a photocell) to initiate a deflection of the electron beam of the cathode ray tube I8 in such a `manner as to produce a horizontal trace A on the screen of the tube. This is accomplished through a sawtooth .wave generator 2i w-hichis under the control of the photocell 20, and an amplifier 22 for applying vthe .saw-tooth potential in amplified form to the lhorizontal deeeting electrodes (not shown) ofthe cathode ray tube. In order to protect vthe screen of the tube and for other reasons `an auxiliary apparatus represented bythe rectangle 23 Vis provided for blanki'ng out the electron beam at intervals when `the vbeamdeiiecting means is not active and also during periods when, after an initial deflection, the beam is being returned to its original starting point. The blanking means employed in this connection are conventional and do not require to be particularly described herein. The nature and function of devices serving this purpose are fully ex- V time required for the reflection of the transmit-.l

ted light-impulse from the distant object tc- 'ward which the transmitting and receiving means are directed. This deflection produces on the screen of the cathode ray tube a trace B which is transverse to the trace A and the relative location of which provides an indication of the distance of the reflecting object.

A light-impulse system of the type so far described po-ssesses an advantage over detecting systems which employ other types of electromagnetic waves in that it may be made very highly directional in character because of the possibility of optically focusing the propagated light rays in a narrowly confined beam. However, considerable difiiculty exists in providing a light-impulse generator capable of developing impulses which are of sufciently short duration to permit the system to function in its intended manner and which at the same time have a sufiicient intensity to permit the detection of impulses reflected from objects at a distance of several miles. In this connection it is particularly important that the duration o-f the generated light-impulse shall be a small fraction of the time required for the reflection of the impulse from'the object under surveillance. If this condition is not fulfilled, a clearly defined indication cannot be obtained on the screen of the cathode ray tube because of ,swamping of the trace produced by the reflected signal through the effects of radiations proceeding directly from the transmitting apparatus.

Another factor which is important to the successful operation of a system of the type under consideration consists in the possibility of obtaining light-impulses having a very steep wave front, that is to say, a very abrupt rise from Zero light intensity to maximum light intensity. For example, if distance measurements are to be made with an error of less than 5G feet, the light-impulse generating system must be of such character as to produce an impulse which attains its maximum value in a time less than that re- -quired for light waves to travel about 25 feet.

In view of the tremendous velocity of light, this obviously signifies a very steep wave front indeed.

The requirements stated in the foregoing are Very satisfactorily fullled by the use of a light generator of the character illustrated in Fig. l. This comprises a pair of mutually spaced electrodes fic, fil-l adapted to be intermittently supplied with discharge current from a high capacity charge-storage agency. In the arrangement shown in Fig. 1 theV charge-storage agency is il- Vlustrated as comprising two banks of series-con- -nected condensers 43 and 44, which banks are connected in parallel across the electrodes 4S and .is in the form of a metal cylinder Gil. `inder is closed at one end by means of a semi- Vspherical glass window E! which is secured to -the extremity of the cylinder by means of a shall be of gas-tight character. `cylinder t8 remote from the windo-w 6l is closed -v pressure.

point, it is the main function of the gaseous lling Y to provide a suitable atmosphere for a light-producing discharge to be produced within the en- 4l. One terminal of the condenser assembly is indicated as a bridging conductor 45 and the other terminal comprises the wall structure of a conductive container 41 which closely surrounds the condenser assembly. Electrode 4G is directly connected to the terminal 4G and the electrode 4l is supported from one end of the cylinder 'i1 as indicated.

For the purpose of charging the condenser assembly there is provided a high voltage transformer 59 which is connected through a regulating inductance 5l to an alternating current supply source 52. The secondary of the transformer 5G is connected to the terminals of the condenser assembly through conductors 5e and 55, the conductor 55 being insulatingly sealed through the wall of the container All' and being in series with an interference suppressing resistor 51 which connects to the condenser terminal 4S.

In the operati-on of the system thus provided the condenser assembly is charged at each cycle of the alternating potential supplied from the transformer EG. The electrodes d and il! are so adjusted that the gap between them can break down just before the condensers attain maximum charge, whereby one discharge is produced during each full cycle of potential reversal. Because of the extremely low inductance of the circuit in which the condensers and the electrodes are included, the resultant spark between the electrodes is of extremely short duration. Moreover, since all the energy of the condensers is discharged within this very brief interval of time, the intensity of the resultant light-impulse is extremely high, reaching in some cases 50,000 Watts of peak output or even higher. These advantageous results are a function of the nature of the light-generating apparatus employed, and

for this reason it is desirable to consider in somewhat greater detail the construction of a partic- -ular light generator which we have successfully vused. Such a generator is represented in Figs. 2

and 3 of the drawing. Y

The construction shown in Fig. 2 comprises an elongated container of which the principal part This cylclamping ring S2. Suitable gasket material 63 is provided in connection with the edge of the window part 6I to assure that the resultant joint The end of the by the combination of a heavy annular ring S5, which is Welded to the cylinder, and a tapered insulator 61 held in vacuum-tight relation with respect to the ring GS by means of a clamping ring 69 and a gasket joint lo. The resultant gas-tight enclosure is iilled with a gas under As will appear more clearly at a later closure. For the purposes of the present invention it is preferred to use in this connection nitrogen or one of the rare gases such as argon or .,gitudinally with respect to it there is provided sembly of condensers '13.

a charge storage system in the form of an vas- These condensers are arranged in four rows or charge-storing units which are positioned symmetrically with respect to the axis of the cylinder 60 (see Figji and .the individual condensers of which areconne'cted ln series by means of bridging 'strapsv'l extending between adjacent terminals of theconde'n'sers. The screws or bolts 'il which are employed to 'secure the bridging straps to the condenser terminals may advantageously extend through the condenser structure so 'as to facilitate mounting the various condensers on insulating mounting rings i9 positioned within the condenser .assem-f bly.

One terminal of each 'of the ycondenser 'rows is connected to a centrally positioned conductive body Si! which thus provides a 'common `clmnection point for the condenser 'assemblyas va whole. This connection may be made, ffor example, by means of bolts '82 which 'are respectively Ain contact with the terminals of the v-e'nd 'condensers of each row and which extend into 'screw-threaded engagement with the Ymetal body 80. The cylindrical casing 60 is made to vvserve as a common connection point for the other end of the conden'ser assembly by connectingit tothe terminals of the'condens'ers at the extremities of the various condenser rows as indicated at 84.

Each of the condensers 13 is preferably made of a flat electrode construction (as distinguished from a spirally wound construction) iso that the internal inductance of each condenser is inherently small. The preferred 'construction is illustrated in Fig. 4 which shows on Aan enlarged scale a longitudinal section of one of the con 'densers i3, the thickness of the internal elements being greatly exaggerated for purposes of clarity.

The condenser includes a large number `of interleaved metal electrodes which are suitably formed of aluminum foil and which vare separated by mica sheets 8e. Every other electrode is in contact with a metal bushing `81 while the alternate electrodes connect with -a bushing te, the two bushings providing externally 4accessible terminals for ythe condenser. The active ypar-ts of the condenser are encased in an insulating substance such as a synthetic resin.

The arrangement of the condensers withinvthe cylinder Se is such that the various condenser rows are relatively close to theinternal lsurface of the cylinder. Since the cylinder provides the return path for current flowing from the ter-l minal 8B through the condenser assembly, the

loop inductance of the -completecircuit measured between the terminal l86 and a "closely adiacent point on the cylinder 66 is very low. rlhis circumstance is made use oi in connection with the present invention by mounting -discharge elec` trodes 9E! and Si in direct electrical connection with the condenser terminal AS 'and-with the metal cylinder 653, the rst such connection being through a short, conductive rod 9.2 which extends outwardly 'from the terminal rlll and the second connection being through an apertured metal wall part 93' which is in direct contact with the end of the cylinder 6U. By virtue of this disposi'- tion of the parts the entire condenser discharge circuit, including the electrodes vand 3|, is of extremely small inductance (in aparticular case about .05 microhenry as compared with a capacity of .01 microfarad for the condenser bank). Accordingly., once the condensers are charged,

they may be abruptly discharged through the electrodes to produce an intense spark of remarkably short duration (i. e. less than one microsecond).

"The electrodes 90 'and '9|"lnay suitably be fc'on- K 'stituted o'f a low work function metal, such asv 6 aluminum. When they are so constituted sand when employed in a gaseous discharge medium, such as iriitrogen, argon or neon, breakdown betweenthem may be causedftooccur automatically whenever 'the impressed voltage exceeds a value readily attainable vwith aA condenser assembly of the type illustrated. ln a particular case, it vhas been vfound 'possible to produce vsuccessive discharges-'by repetitively charging the parallel connected condense-r banks to 'a voltagenn the iorder of v10,000 to 20,000 volts. The impulse 'discharges thus resulting prove to be of highly luminous quality, yielding in `'some cases `a peak intensity of 50,000 watts or more.

assembly from an external Voltage source, a lead- -in vconductor 95 is 'sealed through the Yextremity lof the insulator 81, being connected to the .tere

ininal 80 within the sealed enclosure through the intermediation of a series of current-limiting v.refsistors 91. A connection to the other terminal of the condenser assembly may obviously befm'ade by anixing a conductor (not shown) to Athe sur face of the metal cylinder t0 or .any associated metal part.

In order insulatingly to separate the resistors Q1 from the condensers 13 and thus to .minimize the likelihood of undesired breakdown, an axially extending insulating cylinder JHM] is interposed between them. -A larger insulating cylinder, indicated at lill, is interposed -between the Vcondenser assembly -and the .inner wall surface of v.the metal cylinder Si) fora similar purpose.

The mode of use of a light-impulse generator of the character shown in Fig. 2 hasalreadybeen explained in connection with lthe description .of Fig. 1. In applying the `generator of Fig. 2 'to the system of Fig. 1 it will be understood that the electrodes 9e and 9| correspond to the :electrodes |38 and lll, the condensers T3 to the condensers d3 and "44, etc.

A system of the character ldescribed is applicable to the detection and location of aircraft,i to cloud height measurement, and to distance measurement generally. Under certain circumstances, it also has utility rfor marine purposes in making sub-'surface observations, for example, in the detection and location of 'submerged submarines. y

While the invention has been described by reference to 'a particular :embodiment thereof, it will be understood that numerous 'changes may be made bythose'skilled in the art withoutdepartn ing from the invention. We, therefore, desire in the appended claims to cover all such variations as come within the true spirit and scope of the foregoing disclosure.

What we claim as new and desire to -seoure by Letters Patent of the United States is:

1. In a system in which light l.impulses are `transmitted to a distant object :and thereafter corresponding reflected impulses are received from said *object in a time dependent upon -the distance to the object, the combination which comprises a charge-storing agency, mea-ns for periodically charging the said agency, a--spark discharge type of light source, and v`circuit 'conneetions between the charge-storing agency and the light source for allowing the intermittent dis' aeoacso of such impulses from the aforesaid distantobject.V t, c v' 2. In a system in which light impulses are transmitted to a distant object and corresponding reflected impulses are thereafter received in a time dependent upon the distance vto the object, the combination which comprises a chargestoring agency of small internal inductance, means for periodically charging the said agency, a pair of gas-immersed electrodes positioned in close physical proximity to the Acharge-storing agency, `and direct conductive connections between the terminals of said agency and said electrodes for allowing the intermittent discharge of the former through the latter, the resultant discharge circuit being of such small inductance that the duration of each light impulse generated between the electrodes, upon the occurrence of a discharge is a fraction of the time required for reflection of said impulses from the aforesaid distant object. l Y

3. In a system in which light impulses Aare transmitted to a distant object and corresponding reflected impulses are thereafter received in a time dependent upon 'the distance to the object,

.the combinationv which includes an enclosing casing having .a light-transmitting wall part, a charge-storing agency within the casing, means for periodically charging the said agency, a pair of mutually spaced electrodes within the casing adjacent to the said light-transmitting wall part and inV close proximity to the charge-storing agency, and direct conductive connections between the charge-storing agency and the said electrodes for allowing the intermittent discharge of the former through the latter, the resultant discharge circuit being of such small inductance that the duration of each of thelight impulses generated upon the occurrence of a discharge is a fraction of the time required for reflection of said impulses from the aforesaid distant object.

4. In a system in which light impulses are transmitted to a distant object and corresponding reflected impulses are thereafter received from said object in a time dependent upon the distance to the object, the combination which includes a condenser assembly aranged so thatY current flow is from end to end through the assembly, terminal means for the assembly at its respective extremities, a circuit including said tel"- minal means for periodically charging the assembly, a conductive structure closely surrounding the assembly and extending lengthwise of it, a rst sparking electrode having a direct conductive connection to the said structure near one end thereof, a second sparking electrode directly connected to the vassembly terminal means which is near said one end of the conductive structure, and a connection between the remaining assembly terminal means and the other end of the conductive structure, the resultant loop circuit from the condenser assembly through the sparking electrodes being of such small inductance that the duration of each of the light-pulses generated by discharge of the' assembly through the electrodesis a fraction of the time required for reflection of such impulses from the aforesaid distant object. Y

5. A light impulse generator comprising an enclosing casing, a charge-storing agency within the casing, a pair of mutually spaced electrodes within the casing in proximity to the charge-storing agency, a light-transmitting wall part incorporated in said casing adjacent to the said electrodes, and low inductance conductors-directstoring unitswthin said metal casing and extending longitudinally thereof so that current flow 1y connecting the terminals of the charge-storing spect to the rst electrode `and directly connected' to the assembly terminal means which is near said one end of the conductive structure,'and a connection between the remaining assembly terminal meansand the other end of the conductive structure, whereby the loop circuit through the condenser assembly Y and the conductive structure provides a low inductance discharge path from the assembly to the said sparking electrode.

'7. A light-impulse generator comprising a condenser assembly of elongated hollow configuration, said assembly including a plurality of capacitive units arranged so that current flow is lengthwise through the assembly, terminal `means for the assembly at its respective extremities, a conductive casing closely surrounding and extending from end-to-end of the assembly, a first sparking electrode having a direct conductive connection to the said casing near one end thereof, a second sparking electrode cooperatively spaced with respect to the first electrode and directly connected to the assembly terminal means which is near said one end of the casing, and a connection between the remaining assembly terminal means and the other end of the said casing, Vwhereby the loop circuit through the condenser assembly and the casing providesa low inductance discharge path from the assembly through the said sparking electrodes.

8. A light impulse generator comprising an assembly of charge-storing units extending parallel to a common axis, said assembly having at one end thereof a common connection point to which the adjacent extremities of the various chargestoring units are connected, a conductive structure closely surrounding the assembly and extending from end-to-end thereof, said structure providing a common connection point for the Various charge-storing units at the end of the assembly remote from the first-named connection point, cooperatively spaced electrodes located adjacent to said first-named connection point, a direct conductive connection between one of said electrodes and said first-named connection point, and a direct conductive connection ybetween the other electrode and an adjacent pointof said conductive structure, the resultant discharge path from the said assembly through the electrodes being of such small inductance that the assembly is enabled, upon charging, tocreate between the elec- .trodesa light-producing spark of extremely short duration.

v9. Alight impulse generator comprising a gaslled metal casing having a light-transmitting window at one end thereof, an assembly of chargethrough the assembly. is lengthwise of the casing, said units havinga common connection-point at the end of the casing adjacent the said window and a complementary common connection point for the other end of the assembly being provided by the casing itself, a pair of mutually spaced electrodes within the casing and in proximity to the said window, a first conductive means connecting one ci :aid electrodes directhT to said iirstnamed common connection point, and a second conductive means connecting the other electrode directly to the wall of the casing, whereby a low inductance current path is provided between the charge-storing assembly and the electrodes.

10. A light impulse generator comprising a gaslled metal casing having a light-transmitting window at one end thereof, an assembly of charge-storing units arranged in hollow configuration within the casing and extending longitudinally thereof so that current flow through the assembly is lengthwise of the casing, said units having a common connection point at the end of the casing adjacent to the said window and a complementary common connection point for the other end of the assembly being provided by the casing itself, conductive means sealed through said casing at the end thereonF remote from said window and. extending longitudinally of the casing within said charge-storing assembly, said conductive means connecting with the assembly at said first-named common connection point and serving as an element of a supply circuit for charging the assembly, a pair of mutually spaced electrodes within the casing and in proximity to the said window, a iirst conductive member connecting one of said electrodes to said first-named common connection point, and a second conductive member connecting the other electrode directly to the wal1 of the casing, whereby a low indue-tance discharge circuit is provided between th-e charge-storing assembly and the electrodes.

VICTOR H. FRAENCKEL. SIEGFRIED HANSEN. 

